The present invention relates to a transmitter device, receiver device, and high-frequency amplifier employed in these devices, and is particularly suitable for transmitter devices for carrying out transmission power control or receiving devices for changing receiving power levels.
FIG. 1 shows a typical block structure of a receiving system and a transmitting system for a wireless communications terminal. First, the receiving system is constructed as follows.
Electromagnetic waves received by an antenna 61 are provided to a receiver amplifier 63 by a duplexer 62 after having been converted into a high-frequency electrical signal. A high-frequency electrical signal amplified by the receiver amplifier 63 is made into an intermediate frequency signal by mixing with a local frequency from a local oscillator 65 at a mixer 64. The gain of this intermediate frequency signal is controlled by an intermediate frequency variable gain amplifier 66. In particular, the output level of the intermediate frequency variable gain amplifier 66 is detected by the coupler 68a and the AGC 68 variably controls the gain of the intermediate frequency variable gain amplifier 66 in response to the detected level so that an AGC (Automatic Gain Control) operation can be carried out for the intermediate frequency variable gain amplifier 66.
The AGC 68 generates received signal strength information S1 from the output level of the intermediate frequency variable gain amplifier 66.
The output of the intermediate frequency variable gain amplifier 66 is demodulated by a demodulator 67 to give a baseband signal. This baseband signal is then provided to a baseband signal processor 69, with a speaker 69a then being driven, and audio being outputted.
The transmission system is constructed as follows. First, the audio signal is converted into an electrical signal by a microphone 69b. This output is then provided to a baseband signal processor 69.
A transmission baseband signal outputted from the baseband signal processor 69 is modulated at a modulator 71 and is then amplified at a prescribed gain at an intermediate frequency variable gain amplifier 72. This signal is then mixed with a local frequency from a local oscillator 65 at a mixer 73 to give a high-frequency signal (wireless frequency signal) and is amplified at a radio frequency variable gain amplifier 74. The signal is then amplified at a transmission power amplifier 75, provided to the antenna 61 from a duplexer 62, and is transmitted.
Transmission systems constructed in such a manner that transmission power control is carried out based on received signal strength level information S1 or based on an instruction signal S2 from a remote station such as a base station are common.
For example, an instruction signal S2 included in a receiving signal is provided to a controller 70 after being demodulated at the baseband signal processor 69. The controller 70 then outputs an instruction to a transmission power controller 76 based on the instruction signal S2. The transmission power controller 76 generates transmission power control information S3 based on an instruction from the controller 70 and provides this to the intermediate frequency variable gain amplifier 72 and the radio frequency variable gain amplifier 74. The gain of the amplifying operation is then set-up at the intermediate frequency variable gain amplifier 72 and the radio frequency variable gain amplifier 74 based on the transmission power control information S3.
Alternatively, constructions are also known where transmission power control information S3 is generated based on the receiving signal strength level S1 from the AGC 68 and this is then provided to the intermediate frequency variable gain amplifier 72 and the radio frequency variable gain amplifier 74.
Cases where control of transmission power is carried out using these means on the transmission side are common.
The input signal level to the receiver amplifier 63 is changed at the receiving system depending on the distance to the base station which sent the signal and the base station transmitted signal level. Because of this, the aforementioned AGC control can be used to provide a degree of compatibility with fluctuations in the level of the received signal.
However, in the case of carrying out transmission power control, considering the efficiency for the transmission power amplifier 75 which is the stage following the radio frequency variable gain amplifier 74, there is a problem where there is unnecessary consumption of electric power. Similarly, the operation of the receiver amplifier 63 in response to changes in the receiving signal level strength is not efficient. This problem is described taking the example of the transmission power amplifier 75.
An example of the characteristics of the output power Pout and the Power Added Efficiency PAE for the input power Pin of the transmission power amplifier 75 is shown in FIG. 2.
As can be seen from the drawing, the output power Pout and the Power Added Efficiency PAE increase as the input power Pin increases.
Considering the case where the input power Pin at the transmission power amplifier 75 is lowered due to transmission power control, the Power Added Efficiency PAE is dramatically reduced, as shown in the drawing. For example, the Power Added Efficiency is about 1% when the output is 10 mW, that is 10 dBm and the total power consumption is 1 W. Thus, 990 mW is power dissipated as heat, with there being large room for improvement with regards to lower power consumption.
Technology where a bias voltage or current provided to the transmission power amplifier 75 is controlled in response to transmission power control information S3 is disclosed in, for example, Japanese Laid-Open Patent Publication No. Hei 1-314431 and Japanese Patent Publication Hei. 6-93631 as high efficiency methods for the transmission power amplifier 75 at the time of low output power.
These related bias control methods are described in the following.
An example is given in FIG. 3 where the efficiency at the time of low transmission output is improved by controlling the gate bias of the transmission power amplifier 75 using this transmission power control information S3 while the gain of the intermediate frequency variable gain amplifier 72 and the radio frequency variable gain amplifier 74 is controlled based on the transmission power control information S3.
With the transmission power amplifier 75 of this example, the input power Pin is amplified by an FET 81 at a first stage amplifier via a matching circuit 80a before being further amplified at an FET 82 at a second stage amplifier via a matching circuit 80b. The signal is then outputted as the output power Pout via the matching circuit 80c.
Gate voltages Vg1 and Vg2 are provided to the gates of FET 81 and FET 82 via gate resistors Rg1 and Rg2. Drain voltages Vd1 and Vd2 are applied to the drains for FET 81 and FET 82 and drain currents Id1 and Id2 are made to flow via the choke coils Ld1 and Ld2. The sources of the FETs 81 and 82 are connected to ground.
The gate voltages Vg1 and Vg2 are generated by a gate bias control circuit 83. The gate bias control circuit 83 sets up the values for the gate voltages Vg1 and Vg2 based on the transmission power control information S3.
In this example, the drain current Id can be lowered by changing the value of the voltage Vgs across the gate and source from Vg-on to Vg-on1 as shown in the graph of the voltage Vgs across the gate and source versus the drain current Id of FIG. 4.
The case is considered where the gain of the intermediate frequency variable gain amplifier 72 and the radio frequency variable gain amplifier 74 is controlled based on the transmission power control information S3 and the input power Pin for the transmission power amplifier 75 is small, that is the case during low power is considered. The efficiency can be improved during this kind of low power output by having the drain current Id fall by making the value for the gate voltage Vg of the transmission power amplifier 75 change from Vg-on to Vg-on1 because the desired output can be obtained even if the drain current Id falls.
In this case, as can be understood from FIG. 4, when the value of the voltage Vgs across the gate and source is lowered from Vg-on to Vg-on1, the gain is lowered and the distortion characteristic is inferior because the characteristic for the voltage Vgs across the gate and source versus the drain current Id is not the ideal straight line characteristic. Because of this, considering the permitted gain reduction and distortion characteristics, the reduction from the value Vg-on to the value Vg-on1, i.e. the value taken as Vg-on cannot but be set up and in reality, and the reduction width (control scope of the gate voltage of FIG. 4) cannot be made very large. The drain current Id can therefore not be made too low during low transmission output and the achieved efficiency results will be small.
Another example is shown in FIG. 5. In this example, the structure of the transmission power amplifier 75 is almost the same as that in FIG. 2. However, the gate voltages Vg1 and Vg2 are taken to be fixed values and drain voltages Vd1 and Vd2 are generated by a drain bias control circuit 84. The drain bias control circuit 84 sets up voltage values as the drain voltages Vd1 and Vd2 based on the transmission power control information S3.
The drain current can be lowered and low power consumption can be achieved in this case also during low transmission output by lowering the drain voltage Vd1 and Vd2.
As shown in the graph of the gate/source voltage Vgs and the drain current Id of FIG. 6, the drain current is lowered from the drain current Ids-on to Ids-on1 by changing the value of the drain voltage Vd from Vds-h to Vds-1.
However, the actual scope of variation must also be limited in the case of this method because of lowering of the gain and deterioration of distortion characteristics and only a small improvement in efficiency can be achieved (resulting consumption at low power). In particular, in recent years there has been a tendency for the drain voltage Vds to become lower, with the variable scope of the drain bias therefore becoming smaller accordingly.
Further, there is also a method where the examples of FIG. 3 and FIG. 5 are combined. Naturally, a dramatic improvement in the efficiency results was not achieved.
These related examples where shown in the drawings with single FET elements as the FETs 81 and 82 of FIG. 3 and FIG. 5. However, in reality, the FETs 81 and 82 etc. are constructed as FETs capable of high outputs where a plurality of FET units (FET-1, FET-2, . . . FET-n) are arranged in parallel as shown in FIG. 7.
The structure of these kinds of FET elements when viewed from above is as shown, for example, in FIG. 8.
The signal from the matching circuit 80a of FIG. 7 is inputted to a gate line Gc formed as an upper layer metal layer in FIG. 8. Further, a gate voltage Vg is applied at the gate line Gc via a portion comprising a gate resistance Rg. Eight gate electrodes G1 to G8 are then lead-out from the gate line Gc.
Further, drain electrodes D1 to D4 are formed as lower metal layers, with these drain electrodes D1 to D4 all being connected to a drain line Dc present at the upper metal layer. The drain line Dc is the output line for the FET 81 of FIG. 7.
Moreover, source electrodes S1 to S5 are formed as lower metal layers and are all connected to a source line Sc present at the upper layer metal layer. The source line Sc is then connected to ground.
In this case, drain electrodes and source electrodes are positioned on both sides of each of the gate electrodes G1 to G8. In this way, 8 FET units (FET-1, FET-2 . . . FET-8) are formed.
As the present invention sets out to resolve the aforementioned problems, the object of the present invention is to provide a high-frequency amplifier, transmitting device and receiving device which is simpler and which can achieve dramatically lower power consumption.